Archive for the ‘Security & Saftey’ Category

The circuit of an inexpensive and highly secure electronic security system is explained below. This electronic security system can be used in banks and other high security areas. A normal electronic security system will have a transmitter and a receiver. The transmitter sends out an IR laser and this will be received by the receiver. When an intruder walks past the device, the IR beam is cut and thus the alarm is activated. But, this system has some major disadvantages like limited range and poor line of sight. These disadvantages are eliminated through the PIR sensor circuit explained below. Working…

Gas Discharge Tubes (GDT) – Introduction GDT’s are special type of gas filled tubes used for wide range of electronic/electrical circuits for providing protection against lightning and other power surges. These tubes basically has two electrodes that are kept inside a gas filled closed envelope. In case of electronic applications, the container is mostly ceramic in nature. For high grade electrical applications military tubes are used. The electrical characteristics of this tubes depends on the pressure and composition of gas, and the distance between the two electrodes contained inside. The most commonly used gases in GDT’s are given below. 1)…

Description. This is of course the simplest electronic code lock circuit one can make. The circuit uses one transistor, a relay and few passive components. The simplicity does not have any influence on the performance and this circuit works really fine. The circuit is nothing but a simple transistor switch with a relay at its collector as load. Five switches (S0 to S4) arranged in series with the current limiting resistor R2 is connected across the base of the transistor and positive supply rail. Another five switches (S5 to S9) arranged in parallel is connected across the base of the…

Description. Here is the circuit diagram of a very simple wire loop alarm based on a N-channel enhancement FET 2N700, a buzzer and few passive components.In normal condition the gate of 2N700 (Q1) is connected to the ground through a 100K resistor (R2) and the wire loop. When the wire loop is broken , Q1 will be biased to ON state and the buzzer is activated.The circuit consumes very less standyby current and so the battery will last for a very long period of time. Circuit diagram. Notes. Assemble the circuit on a good quality PCB. The circuit can be…

How to protect IGBT from failures and breakdowns ? Insulated Gate Bipolar Transistors are susceptible to gate insulation damage by the electrostatic discharge of energy through the devices. When handling these devices, care should be exercised to assure that the static charge built in the handler’s body capacitance is not discharged through the device. With proper handling and application procedures, however, IGBTs are currently being extensively used in production by numerous equipment manufacturers in military, industrial and consumer applications, with virtually no damage problems due to electrostatic discharge. IGBTs can be handled safely if the following basic precautions are taken:…

MOSFET requires very careful handling particularly when out of circuit. In circuit a MOSFET is as rugged as any other solid-state device of similar construction and size. MOSFETs have an ultra-thin silicon dioxide layer between the channel and the gate. Because the insulating layer is so thin, it is easily destroyed by excessive gate source voltage VGS. On application of large gate voltage, an open-circuit gate may accumulate enough charge so as to develop an electric field large enough to puncture the thin Si02 layer. Aside due to direct application of an excessive gate-to-source voltage VGS, the thin Si 02…

All MOS devices have insulated gates that are subject to voltage breakdown. For instance the gate oxide for Motorola CMOS devices is about 900 A thick and breaks down at a gate-source potential of about 100 V. To guard against such a breakdown from static discharge or other voltage transient, the protection networks shown in figure are used on each input to the CMOS device. Static damaged devices behave in different ways, depending on the severity of the damage. The most severely damaged inputs are the easiest to detect because the input has been completely destroyed and is either shorted to…

Description. Here is the circuit diagram of an infrared intrusion detector. Whenever a trespasser cuts the invisible infrared beam an alarm sound will be raised. The arrangement consists of a receiver circuit and a transmitter circuit. The transmitter circuit is based on two TLC555 ICs (IC1 and IC2). The first 555 (IC1) is wired as an astable multivibrator operating at 300Hz.The second 555(IC2) is also wired as an astable multivibrator operating at 36 KHz which can be adjusted by using POT R4.The output of IC1 is given to the reset pin of IC2. So the output of IC2 will be…

Description. Here is a simple circuit switches on a light around 2 hours after midnight, the time at which most of the robberies taking place. This simple circuit is build around a CMOS IC 4060 to obtain the required timing. During day time the LDR has low resistance and keeps the pin 12 of the IC1 high, preventing the IC1 from oscillating. When it is dark the LDR resistance becomes high and the pin 12 of IC1 becomes low and the IC starts oscillating, which indicated by the flashing of LED D3.The values of the timing components R1, R2, C4…

Description. Here is a simple shock sensitive alarm circuit that has many many applications fro home to automobiles.The main application of this circuit is to use it as an anti theft alarm in automobiles.A peizo electric sensor is used as the shock sensor which has to mounted on the door which you have to protect. Here the IC1 LM 3558 is wired as an inverting Schmitt Trigger.The POT R1 sets the threshold voltage of the circuit.R1 is used as a feed back resistor.When not activated the out put from the piezo sensor will be low and so do the output…